Re: Why does the number of rows are different in actual and estimated.

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: "Kevin Grittner" <kgrittn(at)mail(dot)com>
Cc: "AI Rumman" <rummandba(at)gmail(dot)com>, "Claudio Freire" <klaussfreire(at)gmail(dot)com>, "Evgeny Shishkin" <itparanoia(at)gmail(dot)com>, "Andrew Dunstan" <andrew(at)dunslane(dot)net>, "postgres performance list" <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Why does the number of rows are different in actual and estimated.
Date: 2012-12-14 19:22:05
Message-ID: 4673.1355512925@sss.pgh.pa.us
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"Kevin Grittner" <kgrittn(at)mail(dot)com> writes:
> AI Rumman wrote:
>> Does FK Constraint help to improve performance? Or it is only
>> for maintaining data integrity?

> I'm not aware of any situation where adding a foreign key
> constraint would improve performance.

There's been talk of teaching the planner to use the existence of FK
constraints to improve plans, but I don't believe any such thing is
in the code today.

regards, tom lane

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